The Great Falls and Old Dominion Railroad (GF&OD) was an interurban trolley line that ran in Northern Virginia during the early 20th century.

Chartered in 1900 by a group of local landowners and acquired in 1902 by John Roll McLean (owner of The Washington Post) and Senator Stephen Benton Elkins,^[1] the 15-mile electrified railroad began operating from Georgetown in Washington, D.C., in 1906. The first trial run was in March of 1906, but only went as far as Difficult Run and the first scheduled car reached Great Falls Park in Fairfax County, Virginia, on July 3 of that year.^[2] They laid a second track in 1908.^[3]

From Georgetown, the railroad crossed the Potomac River on a superstructure built on the upstream side of the old Aqueduct Bridge to Rosslyn in Arlington, where it made connections with an older electric trolley line, the Washington, Arlington & Falls Church Railway (see Northern Virginia trolleys).^[4] From Rosslyn, the railroad traveled northwest along the north side of Lee Highway (now part of U.S. Route 29) to Cherrydale and then on its own right-of-way (now Old Dominion Drive, Virginia State Route 309) in Arlington and Fairfax Counties through forests, farmland and fruit orchards, bypassing the existing villages of Lewinsville and Langley.^[5] At Great Falls, the GF&OD constructed a trolley park, which became a popular destination.

The owners gave their own names to two stations located at the railroad's crossings of major roads: McLean Station at Chain Bridge Road (Virginia State Route 123) and Elkins Station at Old Georgetown Pike (Virginia State Route 193). The station at Chain Bridge Road became a focus for development that evolved into the community of McLean, Virginia.

In 1911, McLean and Elkins incorporated the Washington & Old Dominion Railway (W&OD) and in 1912, the new W&OD signed a 50-year lease on the Southern Railway's Alexandria-Bluemont line. In the same year, it then constructed a double-tracked Bluemont Division connecting line that traveled between two new junctions in Arlington: Bluemont Junction on the Alexandria-Bluemont line and Thrifton Junction on the Georgetown-Great Falls line. The Georgetown-Great Falls line became the Great Falls Division of the W&OD, sharing trackage with the W&OD's Bluemont Division between Rosslyn and Thrifton Junction. In 1935, Fairfax and Arlington counties obtained the right-of-way west of Thrifton Junction in settlement of delinquent taxes. Most of the right-of-way was converted into Old Dominion Drive.

Not much remains of the Great Falls Division.

The right-of-way west of Thrifton Junction became Langston Blvd (formally Lee Highway) and Old Dominion Drive; and the right-of-way between the Key Bridge and Thrifton Junction became Interstate 66. The trestle over Difficult Run lasted until 1979, when it was replaced because it could not handle the loads required of it.^[6]

Great Falls Trolley Park became Great Falls Park, part of the National Park Service.

Several area names, like the town of McLean, also remain.

The stations on the Great Falls Division of the W&OD (with locations of sites in 2008) were:

• Northern Virginia Trolleys
• Washington and Old Dominion Railroad